Water flooding method



Dec. 2, 1958 M. R. TEK

WATER FLOODING METHOD Filed April 6, 1956 INVENTOR. M R TEK 1:0... mmb

BY di ATTORNEYS United States Patent O WATER FLOODING METHOD Mehmet R.Tek, Bartlesville, Okla., assignor to Philiips Petroleum Company, acorporation of Delaware Application April 6, 1956, Serial No. 576,674

Claims. (Cl. 166-10) This invention relates to a process for producingoil from an oil-b earing formation by applying water drive thereto.

lProduction of oil rfrom underground oil-bearing formations by waterflooding is a current practice in the petroleum industry. This method isusually applied as a secondary recovery method but is also applicable toprimary production. After a substantial portion of the oil in theformation has been recovered by other means, residual oil is frequentlyrecovered by injecting water into a series of bore holes or wellssurrounding a somewhat centrally located well (producing well) andforcing the water radially or horizontally toward the producing well soas to drive oil thereto.

In Water flooding as currently practiced a number of problems ordifficulties arise which lower the economic advantage of this type ofoil recovery. There is a very slow response inthe way of oil productionto water hooding as currently practiced, necessitating a great deal ofeffort and expense in saturating the formation before any appreciablequantity of oil is produced. In many formations subjected to waterflooding, channeling interferes with the displacement of oil from largesections of the formation. There is a long ood-out time which adds tothe cost of oil production and defers the time at which the productionprogram yields a financial return. Another disadvantage lies in the factthat conventional water flooding results in the by-passing of largeareas which contain appreciable amounts of recoverable Oil. Otherdisadvantages in water ooding are known to those in the industry.

The invention is concerned with a method or process for recovering oilby water drive which eliminates or minimizes the above enumerateddisadvantages inherent in current water flooding techniques.

Accordingly, it is an object of the invention to provide an improvedmethod for oil recovery by water flooding. Another object is to providea method of oil recovery which utilizes vertical water drive. A furtherobject is to provide oil recovery by water drive which eliminates orminimizes any of the problems inherent in currently practiced waterflooding. Other objects of the invention will become apparent from aconsideration of the accompanying disclosure.

The method of the invention comprises forming horizontal fractures in anoil-bearing formation at substantially different levels so that thefractures at one level overlap, at least in part, the fractures at theother level; injecting water into the fractures at one level to till thesame and form a pancake-type water layer; and thereafter applyingpressure to the water layer to force water thru the formation to thefractures at the other level, thereby driving oil thereto so that it canbe recovered from a bore hole or production well penetrating theformation in the area of the fractures into which water is not initiallyintroduced. The preferred procedure comprises fracturing the oil-bearingformation around a centrally positioned production well surrounded by anumber of injection wells 2,862,556v Patented Dec. 2, i958 and alsofracturing the formation around the injection wells at a substantiallydifferent level in the formation than the level of the fractures in theproduction well. The fractures in the formation around the injectionwells are preferably made at a lower level or adjacent the bottom of theformation and the fractures around the production well are made at ahigher level or adjacent the top of the formation so that the waterdrive is upwardly from the fractures at the lower level to the fracturesat the higher level, thereby taking advantage of the buoyancy of oil inWater. However, it is feasible to operate in the reverse manner and maybe advantageous to do so in certain applications and formations.

ln most oil bearing formations the permeability is sufciently low tooffer substantial resistance to water flooding but upon fracturing theformation the water readily flows into the fracture to form a thin layerof water extending over an appreciable area surrounding an injectionwell. In the process of the invention where a fractured area overlapsthe pancake-type water layer, continued application of hydraulicpressure to the water layer provides a very effective linear verticalwater drive of the flood front which effects substantially an immediateyield of oil from the water flooding eiort with a minimum consumption ofwater. Ordinarily after the injection fractures are lled with water andpressure is applied to force the water through the formation there iscompetition between radial ow at the periphery of the fracture andvertical ow; however, the vertical distance between the upper and lowerfracture levels is relatively short so that even though the penetrationradially from the periphery of the water layer is equal to the distancebetween the two fracture levels, the water loss is relativelyinsignificant. A factor which tends to minimize the peripheral radialflow of water is the lower pressure drop between the fracture levels ascompared to the pressure drop horizontally thru the formation for asubstantially greater distance. This assumes, of course, that theresistance to horizontal flow thru the fractures is substantiallynegligible. In order to obtain adequate vertical ilow from one fracturelevel to the other, it is only necessary that the input pressure exceedthe formation pressure by at least the hydrostatic head of the verticaldrive esired. Practically, however, if recovery over the entire area offracture is desired the input pressure should be additionally increaseda calculated amount to compensate for the pressure drop betweenfractures.

A more complete understanding of the invention may be had by referenceto the schematic drawing which shows a broken vertical section throughan oil bearing formation penetrated by bore holes or wells and fracturesin accordance with the invention.

Referring to the drawing, wells i@ are utilized as water injection wellsland penetrate to a evel the bottom of the oil bearing formation l2,while the well i4 is a producing well and penetrates the formation to anupper level thereof near the top of the formatiert. The formation isfractured by any suitable means, such as by hydraulic fracturing, aroundproducing well lil as shown at 16 and the formation is also fracturedaround injection Wells lll as at i8 so that fracture i6 overlaps asubstantial portion of fractures 18. it is to be understood, of cou thatother water injection wells surrounding well le are fractured in themanner shown for weils l0. The 5 or 7 spot pattern or any other suitablewell pattern may be utilized in recovery of oil by the method of tinvention. After the fracturing is effected `around the injection andproducing wells at the desired levels, water is injected by conventionalmethods through wells if; so as to fill the fractures with water andthereby forrn or establish a series of pancake layers of water in thefractures around the injection wells in a pattern surrounding theproducing well. At this point additional pressure is applied to thewater in the injection wells and in the fractures extending outtherefrom so as to force water upwardly toward fracture 16 and therebydrive oil from the lower section of the formation upwardly to fracture16. As this procedure continues the -oil-Water interface 20 progresses`upwardly until water reaches fracture 16 and the oil driven from theformation is recovered thru well 14.

Certain modifications of the invention will become apparent to thoseskilled in the Iart and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A process for applying water drive to an underground oil-bearingformation which comprises horizontally fracturing said formation at alower level therein around at least one well; horizontally fracturingsaid formation at an upper level therein around at least one additionalwell so that the upper and lower fractures overlap; forcing water intothe formation thru the fractures at one level so as to drive oil in saidformation toward the fractures at the other level; and recovering oilfrom said other level.

2. The process of claim 1 wherein water is forced into the fractures atsaid lower level and oil is recovered from 2 of said formation andaround a centrally positioned production well near the top of saidformation.

4. A process for applying water drive to an underground oil-bearingformation substantially free of vertical fractures which compriseshorizontally fracturing said formation at an upper level therein arounda production Well; horizontally fracturing said formation at a lowerlevel around a plurality of wells surrounding said production well sothat the upper and lower fractures overlap; introducing water to thelower fractures and forcing same toward the upper fractures so as todrive oil to said upper fractures and to said production Well.

5. A process for producing oil from an oil-bearing underground formationwhich comprises forming horizontal fractures in said formation atsubstantially different levels therein so that the fractures at onelevel overlap, at least in part, the fractures at the other level;injecting water into the fractures at one level to fill same and form apancake-type `water layer; and applying pressure to force water fromsaid layer thru said formation to the fractures at the other level so asto drive oil to last said fractures.

Dismukes Aug. 24, 1954 Spearow July 17, 1956

